OBJECTIVE To assess the effect of advancing age upon the relationship between leptin and body fat in rhesus monkeys. RESULTS In rhesus monkeys, as in humans, leptin is positively correlated with body fat content, however, this relationship changes with advancing age. DISCUSSION Serum leptin concentration is positively correlated with body fat content. The effect of advancing age upon the relationship between leptin and body fat is not well known. In this experiment, 115 adult rhesus macaques (60 females, 55 males) ranging in age from 4 to 34 years old were evaluated for body composition and leptin concentrations. Body composition was determined by dual-energy X-ray absorptiometry. Serum leptin was measured in single fasted morning blood samples. Results indicate no sex difference in the way age interacts with leptin and body fat, allowing sexes to be pooled for further analysis. Pearson product moment correlations showed leptin to be highly correlated with indices of body fat (total fat, r=0.802; %fat, r=0.783; abdominal fat, r=0.801; thoracic fat, r=0.778). Multiple regression analysis showed an increase in leptin with age(p=0.0008), and an interaction between leptin and total body fat with age (p=0.006). This study confirms previous findings of a close relationship between circulating leptin levels and indices of body fat. In addition, this experiment shows that in rhesus monkeys, the relationship between leptin and body fat is not influenced by gender, but does change with advancing age. FUTURE DIRECTIONS We plan to continue using DXA and leptin to better characterize body composition in rhesus monkeys, and to continue to explore the relationship between body composition and leptin at different ages. KEY WORDS fat tissue mass, body fat distribution, DXA FUNDING NIH PO1 AG11915 PUBLICATIONS Colman RJ, Ramsey JJ, Kemnitz JW. The effects of age and body composition on serum leptin levels in rhesus macaques. Gerontol 38(1):15, 1998.